A slide I read at the end of a tutorial by Matthew Flatt
indicates a key focal point.
This is the tutorial:
http://www.cs.utah.edu/classes/cs6520-mflatt/s04/macro-tutorial.pdf
The slide read:
There is no one scheme.
or
Scheme is a language for defining practical languages.
Standardized language declaration syntax may be the way to
tame implementation differences.
amen to that.